1. Field of the Invention
The present invention relates to a heat exchanger mounted on a motor vehicle and to, for example, a heat exchanger used as a radiator or heater core.
2. Background of the Related Art
Japanese laid-open utility model S54-6664 and Japanese laid-open utility model S63-159669 disclose a laminated heat exchanger 700 as shown in FIG. 30 and FIG. 31 wherein tubes 702 are formed by laminating a plurality of fin plates 701. Each fin plate 701 has a tapered cylindrical portion 703 formed by drawing. The cylindrical portions 703 are aligned in the vertical direction in the figure. The tubes 702 in this type of laminated heat exchanger 700 are formed by laminating and joining a plurality of fin plates 701.
In this type of laminated heat exchanger 700, to maintain the strength of the joint between the adjoining cylindrical portions 703 to thereby prevent the adjoining cylindrical portions 703 from separating from each other, the cylindrical portions 703 project from the flat surfaces of the fin plates 701 by a relatively large amount to maintain the surface area in which the adjoining cylindrical portions are joined.
However, in the conventional laminated heat exchanger 700, the thickness CB1 of each tube 702 (refer to FIG. 30 and FIG. 31) becomes large when the cylindrical portions 703 are projected from the flat surfaces of the fin plates 701 by a relatively large amount as described above.
This increases a pressure loss in the air flowing between the tubes 702, thereby reducing the flow capacity of the air flowing through the core portion 704. In addition, the proportion of the fin plates 701 to the whole core portion 704 is reduced. This has resulted in a problem in that the efficiency of the heat exchange between the air and the engine cooling water and, consequently, the heat radiating performance of the fin plates 701 is degraded.
An object of the present invention is to provide a heat exchanger wherein the heat radiating performance of the fin plates is improved by improving the heat exchange efficiency.